Volumetric Computed Tomography Reconstruction, Rapid ... · museum, evaluating pros and cons of the...

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Int. J. Morphol.,37(3):838-844, 2019.

Volumetric Computed Tomography Reconstruction, Rapid Prototyping and 3D Printing of Opossum

Head (Didelphis albiventris)

Reconstrucción Volumétrica por Tomografia Computarizada, Prototipado Rápido e Impresión 3D de Cabeza de Zarigüeya (Didelphis albiventris)

Catia Helena de Almeida Lima Massari1; Ana Carolina Brandão de Campos Fonseca Pinto2;

Yuri Karaccas de Carvalho3; Adriano Ferreira Silva1 & Maria Angélica Miglino2

MASSARI, C. H. A. L.; PINTO, A. C. B. C. F.; DE CARVALHO, Y. K.; SILVA, A. F. & MIGLINO, M. A. Volumetric computedtomography reconstruction, rapid prototyping and 3D printing of opossum head (Didelphis albiventris). Int. J. Morphol., 37(3):838-844, 2019.

SUMMARY: Natural anatomical pieces of wild animals are rare and teachers seek alternatives in satisfactory quantity andquality to inform their students. This article aims to describe the use of multiplanar reconstructions and 3D volume rendering computedtomography (CT) images, rapid prototyping and 3D printing of opossum head to create a biomodel to veterinary education in descriptiveanatomy of wild animals. A six-step method study was conducted to construct the biomodel: (1) selection of opossum head from museum;(2) CT scanning of bones structures in veterinary hospital; (3) DICOM visualization medical images in multiplanar reconstructions and3D volume rendering; (4) .dicom file conversion to .stl; (5) 3D printing of opossum head by rapid prototyping; (6) comparison of 3Dmodel printed with the original anatomical piece. The use of CT images with their different forms of reconstruction can provide a morecomprehensive 3D view of opossum craniofacial region and allow a better understanding of head anatomy of this species. The 3Dprinted biomodel can be a viable alternative to original bone specimens when used in anatomy education. However, further studies mustbe continued to validate the method in Veterinary Medicine courses.

KEY WORDS: Veterinary Education; Anatomy; Biomodel; 3D Printing; Opossum.

INTRODUCTION

The white-eared opossum, Didelphis albiventris, canbe considered an excellent model for comparativeembryology in developmental biology studies. The groupMetatheria (Didelphimorphia) has relevance amongmammals, particularly related to reproduction aspects, asthey represent an important transition link betweenPrototheria and Eutheria groups.

But it is not so easy to study the opossums todaybecause of the difficulty to obtain animal corpses in manyveterinary universities. Most natural anatomical pieces ofwild animals are rare and teachers seek alternatives insatisfactory number and gross peculiarity to inform theirstudents. Fortunately, the traditional method of teaching hasundergone innovations time after time. The use of diagnostic

imaging in order to develop virtual anatomical models andthe use of 3D printing to objectify through rapid prototypingthese scanned models is a trend in veterinary anatomyteaching. This didactic alternative is not substitutive for thedissection based teaching but a complement to the traditionalmethod of teaching-learning in anatomy (Massari et al.,2018).

The available literature suggests that both digital andphysical scale models of animal skeletal components can berapidly produced by using 3D printing technology (Li et al.,2018).

Understanding the three-dimensional nature of wildanimal form is imperative for an effective medical practice

1 PhD Student in Anatomy of Domestic and Wild Animals, School of Veterinary Medicine and Animal Science, University of São Paulo (FMVZ/USP),Brazil.

2 Surgery Department, School of Veterinary Medicine and Animal Science, University of São Paulo (FMVZ/USP), Brazil.3 Laboratory of Veterinary Anatomy - 3D Educational Technologies. Federal University of Acre (UFAC), Rio Branco, Acre, Brazil.

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especially in descriptive anatomy where morphology iscompared between different species of domestic and wildanimals. Literature affirms that the emergence of 3D printingcan provide numerous opportunities to enhance aspects ofmedical and healthcare training. These plastic models canbe used in anatomy education as a teaching tool as well as amethod for increasing the curriculum and innovatingestablished learning modalities, integrating anatomy toradiology (Smith et al., 2017).

The creation of new rapid prototyping techniques,the low cost of 3D printers as well as the emergence of newsoftware for image analysis have allowed the creation of 3Dmodels of bones. Truly, its application is possible in the fieldof anatomy teaching in many universities of animal sciences.The deterioration of bone pieces by continuous use, thedifficulty in obtaining a good number of anatomical piecesfor all students as well as the coming up of the 3D printersat an affordable price for the manufacturing of 3D bonesmodels at full scale have led to the introduction of a newway of studying anatomy. The advent of 3D printers hasallowed the creation of biomodels by rapid prototyping,providing production of three-dimensional structures startingfrom a computer graphic modeling and, then, an additivemanufacturing process (Lozano et al., 2017).

Technological resources can contribute to veterinaryanatomy teaching, making subjects related to this area whichare essential for the training of Veterinary Medicine students,increasingly updated in the face of new technologies andnew generations of students. Specific in osteology, today

there are biomodels of canine and equine skeletons reportingthe use of 3D printing to produce them (dos Reis et al., 2017).

This article aims to describe the use of multiplanarreconstruction, volumetric computed tomographyreconstruction, rapid prototyping and 3D printing of opossumhead to create a biomodel to veterinary education indescriptive anatomy of wild animals. The academics needto know gross anatomy of wild animals but unfortunately,they often do not have an available laboratory with asatisfactory collection of anatomical pieces. Currently, themain macroscopic study tool is by comparative anatomyinvestigating the shape and development of the animal bodythrough the analogy between different species.

MATERIAL AND METHOD

This study was developed in the University of SãoPaulo (USP), Brazil, comprising six steps as shown by theflowchart below (Fig. 1).

The first step was borrowing the opossum head fromthe collection of the University's Veterinary AnatomyMuseum (MAV/USP), which made possible to study thebones in situ to know this topographic region. The secondstage comprised a computerized tomography examinationby the Diagnostic Imaging Service- Surgery Department –School of Veterinary Medicine and Animal Science; thecomputed tomographic images were acquired with a Philips

Fig. 1. Flowchart for design of 3D anatomical model. Sequence of six steps to creation of 3D prototyping of opossum head.

MASSARI, C. H. A. L.; PINTO, A. C. B. C. F.; DE CARVALHO, Y. K.; SILVA, A. F. & MIGLINO, M. A. Volumetric computed tomography reconstruction, rapid prototyping and 3D printing ofopossum head (Didelphis albiventris). Int. J. Morphol., 37(3):838-844, 2019.

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CT Scanner MX 8000 IDT® 16 data channels in DICOM(Digital Imaging and Communications in Medicine) fileformat. It was produced in 271 slices thickness of 0,7mm. The third step involved the files analysis in Osirix®and Radiant® DICOM viewers, which allowed to com-pare different sequences: the multiplanar reconstructionsin orthogonal planes (transverse, sagittal and dorsal pla-nes) and the 3D volume rendering that allows the viewof a large volume of data generated by CT scanner inthree-dimensional space and interactively explored indifferent aspects. The fourth step involved the conversionof DICOM file to STL through the software InVesalius®for the creation of the opossum head prototype. The fifthstep was to print the opossum head prototype throughthe 3D printer model Flexprinter® 2025 (available inwww.flexbras.com.br), according to the followingspecifications: layer thickness 0.2 mm, wall thickness 1.2mm, fill 20 %, material ABS color ivory. These were usedto produce a 1:1 scale physical model with the fuseddeposition modeling (FDM) 3D printer to produce highlyaccurate opossum head model using the software Cura®.And finally, the sixth stage comprised the comparison ofthe 3D model with the original anatomical piece of themuseum, evaluating pros and cons of the biomodel created.

RESULTS AND DISCUSSION

Particularly the skull is made of many fused bonesas the animal becomes skeletally mature. CT is anexcellent modality to depict and study the complexanatomy of the skull and the jaws using multi-planar 2Dimages as well as 3D rendering images. The skull isgenerally symmetric along sagittal plane which can beused for comparisons of paired structures duringinterpretation (Wisner & Zwingenberger, 2015).

The opossum skull is relatively small and narrow.It can be divided into two parts: facial or viscerocranium,which comprises a pair of mandibles and bones thatcircumscribe the initial part of the digestive andrespiratory systems, and neurocranium which houses theencephalic organs from central nervous system. Figures2, 3 and 4 show the gross anatomy of bones that composethe head of an opossum.

This research proves that the parts of maxilla andpremaxilla palate are fenestrated by a series of pairedapertures. The external sagittal crest, the most prominentstructure in the dorsal view of the skull, can also bepalpated in a living animal during semiologyexamination.

Fig. 2. Dorsal view of natural bones (left) and 3D-printed bones (right)that compose the head of opossum. 1, nasal; 2, incisive; 3, maxilla; 4,lacrimal; 5, frontal; 6, parietal; 7, occipital; 8, temporal; 9, zygomatic;10, mandibula. Note also: esc, external sagittal crest; za, zygomaticarch; zp, zygomatic process of the frontal bone; fp, frontal process ofthe zygomatic bone. Bar = 5 cm.

Fig. 3. Ventral view of natural bones (left) and 3D-printed bones (right)that compose the head of opossum. Note also: ms, mandibularsymphysis; za, zygomatic arch; mf, maxillopalatine fenestra; pf, palatinefenestra; ch, choana; ap, angular process of mandibula; cp, condylarprocess of mandibula. Bar = 5 cm.

The mandible is definitely the largest bone in the head.However, in this work it was not possible to separate themandible from the skull since it was already found artificiallyglued because it is a very fragile piece exposed in the AnatomyVeterinary Museum.


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When comparing the two pieces (in natura and arti-ficial), the printed template has estimated weight of 21.47grams while the original piece has 23.10 g. The area measuresare similar presenting 9.5 cm of height and 5.0 of width.

The qualitative aspects of rapid prototyping and 3Dprinting regarding structures that can be seen and structuresthat unfortunately cannot be seen when compared to the piecein natura are presented in the Table I.

About dental arch defect observed in biomodel, it isbelieved that the problem actually occurred during 3Dprinting process since the Figure 5 proves that the dentalroots were correctly scanned by CT. The maximum intensityprojection (MIP), projecting the voxel with the highestattenuation value on every view throughout the volume ontoa 2D image makes possible to analyze with a close definitionnot only the tooth but also the gomphosis or the dentoalveolarsyndesmosis.

Fig. 4. Left lateral view of natural bones (left) and 3D-printed bones (right) that compose the head of opossum. 1, nasal; 2, incisive; 3,maxilla; 4, lacrimal; 5, frontal; 6, parietal; 7, occipital; 8, temporal; 9, zygomatic; 10’, mandibular ramus; 10’’, mandibular body. Notealso: nv, nasal vestibule; iof, infraorbital foramen; ct, canine tooth; mf, mentalis foramen; eo, eye orbit. Bar = 9.5 cm.

Table I. Analysis of qualitative aspects of the prototyped piece compared to the natural one. Images from authors.

MASSARI, C. H. A. L.; PINTO, A . C. B. C. F.; DE CARVALHO, Y. K.; SILVA, A. F. & MIGLINO, M. A. Volumetric computed tomography reconstruction, rapid prototyping and 3D printing ofopossum head (Didelphis albiventris). Int. J. Morphol., 37(3):838-844, 2019.

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This kind of defect is not rare when using a 3Dprinter; biomodel presents this dentistry identificationproblem when compared to in natura piece or DICOM fileimages from CT. In the original one, it is possible to delimitclearly the dental roots of some teeth, mainly of thepremolars, whereas in the biomodels the region of dentalarch is not so well identifiable. One of the possibilities forcorrection of this defect can be by applying Meshmixer®,a free software to clean the 3D scan before printing.

Opossums have the following dental formula: I 5/4, C 1/1, PM 3/3, M 4/4, totalizing 50 teeth, according toSilva et al. (2006). They have more incisors teeth in infe-rior dental arch (mandibula) than in superior dental arch.Marsupials have absence of deciduous dentition; its onlydeciduous tooth is the third premolar. In this study it waspossible to observe that the superior canine teeth areextremely well developed for hunting.

The opossum skeleton basically follows the patternof all other mammals. However, the literature points atdistinguishing characteristics related to the locomotor systemlike the presence of epipubic bones (Silva et al.) and theabsence of a true patella. After all, there was no significantdifference between bones found in head of the white-earedopossum when compared to those described for dogs.

In this study, CT proved to be an important teaching-learning resource as it becomes more advanced for animalpatients and available for students of Veterinary Medici-ne. It can also dissect virtually some extremely fragile orhard-to-reach regions in anatomical pieces and to improveteaching on complex spatial interactions. The multiplanarand 3D postprocessing techniques demonstrated thefeasibility of generating virtual models, being a teaching-learning tool that offers an opportunity to study anatomicalpieces that are often rare in veterinary anatomy laboratories.

The use of CT images with their different forms ofreconstruction can provide students with a more

comprehensive 3D view of opossum craniofacial region,allow greater understanding of head anatomy andawareness for the preservation of this important species.And the 3D model of skull obtained using the additionmanufacturing technique in 3D printing with FDMtechnology reproduces the anatomical details that thestudents of anatomy must know, with great accuracy andprecision. The rapid advancement in the design ofincreasingly fast and accurate 3D printers as well as theappropriated software that facilitates their use suggests thegrowing implementation of this technology in the field ofveterinary education.

In relation to the aspects of the biomodel creationitself, the value of US$ 17.00 was spent for the productionof one anatomical piece. The time of creation was of 1h30 min for conversion of the CT image in stereolithographyfile format and the time for the actual printing was of 3h.The quality of slight loss in the printed model was due tothe inexperience of the authors about handling the 3Dprinted biomodel, being recommended the standardizationof this new 3D printer for future works with bones scannedby TC.

The results present so many advantages of biomodelwhen comparing to the preparation of a natural anatomicalpiece through traditional anatomical technique. Firstly, allbones used in animal anatomy studies must be obtainedlegally and it is unquestionable the difficulties today inobtaining corpses of wild animals due to ethical obstaclesand by government agencies regarding the collection ofdead wild animals in forests or roads. Secondly, theanatomical osteotechniques involves bones maceration,drying, assembly of skeletons and application of varnishesto preserve them. These steps must occur in a preparationroom of anatomy laboratory and involve a correctenvironmental disposal of biological material such asremoving soft tissues. All of this certainly involves higherfinancial investments with specialized technical manpower,chemical products, surgical instruments and appropriatefacilities. In addition to this the storage of the natural partsneeds to be in an appropriate place to avoid fungusdeterioration. In face of all this, the biomodeling ofsynthetic bones is less expensive, faster and requires muchless care for the storage of the parts made in polymerizableresins.

Another great advantage lies in the provision of alarge number of biomodels of different species, often notpresent in that geographic region, for an infinite numberof students in short time production. It also allows to somany universities, including those addressed far away fromthe habitat of this species, to access the biomodel.

Fig. 5. Maximum intensity projection (MIP) is a CT method analysisfor opossum dentistry evaluation.


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For learning and teaching gross anatomy practically,a variety of specimen is necessary in quantity that meetsall the academic. Hagebeuker et al. (2018) related to theimportance in producing syntactic didactic material forclasses. They demonstrated that anatomically correctvaluable equine skulls of horses at different ages in differentsizes can easily be produced with the help of 3D printingin any requested number.

Access to adequate anatomical specimens can bean important aspect in learning the anatomy of wildanimals. Moreover, the 3D printed biomodel can be a via-ble alternative to original bone specimens when used inanatomy education. This study demonstrated an importantexample of reproducing bone models to be used in anatomyveterinary education. Schimming et al. (2016) related thatknowledge of the skull morphology in mammals is veryimportant, because it provides baseline anatomicinformation and can improve veterinarian medical andsurgical clinics knowledge.

Due to the existence of few published works using3D manufacture in the area of teaching of the anatomy ofwild animals, certainly this work has an important role inthe disclosure of biomodels as a didactic alternative toveterinary osteology teaching. However, further studiesmust be continued to validate the method in the teaching-learning relationship of academics in veterinary medicinecourses. So, an investigation into the use of 3D-printedanatomical models in undergraduate anatomy educationis suggested in future research certainly because theprogress in the creation of new biomodels will be thegreatest achievement in veterinary education development.

In Brazil, according to Federal Council of VeterinaryMedicine (Conselho Federal de Medicina Veterinária,2018), there are more than 300 undergraduate courses inveterinary medicine today besides other related coursessuch as animal sciences (zootechnic courses) and biologicalsciences (Conselho Federal de Medicina Veterinária). So,3D printing can overcome problems associated with thepoor infrastructure of anatomy laboratories.

This work also presented a multidisciplinary aspectshowing that it is possible to integrate disciplines such asanatomy, diagnostic imaging and surgery (producingspecific biomodels for surgical training). Nowadays, weare experiencing a badly reduction in the workload of theanatomy class in order to increase the workload of disci-plines linked to the medical clinic. Under this point of view,this work can provide a new educational perspective bychanging the traditional teaching method for the integrationof contents.

CONCLUSION

It is concluded that it is possible to mitigate theproblems caused by the restriction of the use of animals ortheir bodies in educational institutions, creating biomodelsto veterinary education. This work certainly reduces theacademic gap between students from universities with largenatural collections and students from beginners’ institutionsespecially in the Brazilian private higher educationnetwork.

ACKNOWLEDGEMENTS

The authors thank the University of São PauloMuseum of Veterinary Anatomy (http://mav.fmvz.usp.br)for lending its collection and Flexbras.(http://impressora3dflexbras.com.br) for the development ofBrazilian 3D printing technology.

MASSARI, C. H. A. L.; PINTO, A. C. B. C. F.; DECARVALHO, Y. K.; SILVA, A. F. & MIGLINO, M. A. Re-construcción volumétrica por tomografía computarizada,prototipado rápido e impresión 3D de cabeza de zarigüeya(Didelphis albiventris). Int. J. Morphol., 37(3):838-844, 2019.

RESUMEN: Las piezas anatómicas naturales de anima-les salvajes son raras y los profesores buscan alternativas satis-factorias, en cantidad y calidad, para enseñar a sus alumnos. Esteartículo tuvo como objetivo describir el uso de la reconstrucciónvolumétrica por tomografía computarizada, la creación rápida deprototipos y la impresión 3D de la cabeza de zarigüeya para obte-ner un biomodelo en anatomía descriptiva de animales salvajespara educación veterinaria. Se realizó un estudio en seis pasospara construir el biomodelo: (1) selección de cabeza de zarigüeyadel museo; (2) tomografía computarizada de estructuras óseas enhospital veterinario; (3) visualización de las imágenes médicasen DICOM por reconstrucciones multiplanares y renderizaciónde volumen 3D; (4) conversión de archivos .dicom a .stl; (5) im-presión 3D de cabeza de zarigüeya mediante prototipado rápido;(6) comparación del modelo 3D impreso con la pieza anatómicaoriginal. El uso de imágenes de tomografía computarizada, consus diferentes formas de reconstrucción, puede proporcionar unavista 3D más completa de la región craneofacial de zarigüeya ypermitir una mejor comprensión de la anatomía de la cabeza deesta especie. El biomodelo 3D impreso puede ser una alternativaviable a las muestras óseas originales cuando se utiliza en la educa-ción de la anatomía. Sin embargo, se deben continuar los estudiospara validar el método en los cursos de Medicina Veterinaria.

PALABRAS CLAVE: Educación Veterinaria; Anato-mía; Biomodelo; Impresión 3D; Zarigüeya.


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REFERENCES

Conselho Federal de Medicina Veterinária (CFMV). Website. Brasilia,Conselho Federal de Medicina Veterinária, 2018. Available in: http://portal.cfmv.gov.br

dos Reis, D. A. L.; Gouveia, B. L. R.; Alcântara, B. M.; Saragiotto, B. P.;Baumel, É. E. D.; Ferreira, J. S.; Rosa Júnior, J. C.; Oliveira, F. D.;Santos, P. R. S. & Assis Neto, A. C. Biomodelos ósseos produzidospor intermédio da impressão 3D: uma alternativa metodológica noensino da anatomia veterinária. Rev. Grad. U. S. P., 2(3):47-53, 2017.

Hagebeuker, K.; Zandt, E.; Wölfel, I.; Weber, S. & Poulsen Nautrup, C.Different forms of equine sculls produced with a 3D printer. Hannover,32nd Congress of the European Association of Veterinary Anatomists,2018.

Li, F.; Liu, C.; Song, X.; Huan, Y.; Gao, S. & Jiang, Z. Production of accurateskeletal models of domestic animals using three-dimensional scanningand printing technology. Anat. Sci. Educ., 11(1):73-80, 2018.

Lozano, M. T. U.; Haro, F. B.; Diaz, C. M.; Manzoor, S.; Ugidos, G. F. &Mendez, J. A. J. 3D digitization and prototyping of the skull for practicaluse in the teaching of human anatomy. J. Med. Syst., 41(5):83, 2017.

Massari, C. H. A. L.; Schoenau, L. S. F.; Cereta, A. D. & Miglino, M. A.Tendências do ensino de anatomia animal na graduação de medicinaveterinária. Rev. Grad. U. S. P., 3(2):25-32, 2018.

Schimming, B. C.; Reiter, L. F. F.; Sandoval, L. M.; Filadelpho, A. L.;Inamassu, L. R. & Mamprim, M. J. Anatomical and radiographic studyof the white-eared opossum (Didelphis albiventris) skull. Pesq. Vet.Bras., 36(11):1132-8, 2016.

Silva, J. C. R.; Dias, J. L. C. & Cubas, Z. S. Tratado de Animais Selvagens.São Paulo, Roca, 2006.

Smith, C. F.; Tollemache, N.; Covill, D. & Johnston, M. Take away bodyparts! An investigation into the use of 3D-printed anatomical modelsin undergraduate anatomy education. Anat. Sci. Educ., 11(1):44-53,2018.

Wisner, E. R. & Zwingenberger, A. L. Atlas of Small Animal CT and MRI.

Ames, Wiley Blackwell, 2015.

Corresponding author:Catia Helena de Almeida Lima MassariUniversity of São PauloSchool of Veterinary Medicine and Animal ScienceSurgery DepartmentPostgraduate Program in Anatomy of Domestic and WildAnimalsAv. Prof. Orlando Marques de Paiva, 87Cidade UniversitáriaSão Paulo-SP 05508-010BRAZIL

Email: [email protected]

Received: 12-12-2018Accepted: 01-02-2019


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